The present invention pertains to processes for the preparation of highly branched polymers and aliphatic-aromatic polyesters. More particularly, the present invention pertains to multiply-branched polyesters and processes for the preparation of multiply-branched aliphatic-aromatic polyesters.
Highly branched, non-crosslinked polymers have been prepared by "multiple generation" and "single generation" procedures. The multiple generation procedures are exemplified by Tomalia, D. A., et al, Angewandte Chemie, International Edition in English, 29, 138-175 (1990) and U.S. Pat. No. 5,041,516 to Frechet, J. M. J. et al, which describe the preparation of highly branched, non-crosslinked polyamidoamines and polybenzyl ethers, respectively. Tomalia et al identified the polymers produced as "starburst polymers" or "starburst dendrimers". Both publications describe preparations in which the macromolecules were prepared by repeatedly reacting, isolating and purifying a product through a series of growth steps. The product of each growth step is called a "generation". These procedures are highly laborious, but the product produced is highly uniform. Newkome et al, Journal of the American Chemical Society, Vol. 112, 8458, (1990) describes a similar step and repeat process used to build up various macromolecules described as tree-like and identified as "arborols".
Single generation procedures are much less laborious than multiple generation procedures. The single generation procedures are exemplified by Flory, P. J., Journal of the American Chemical Society, 74, p.2718 (1952), which presents a theoretical analysis of the formation of highly branched, soluble polymers from monomers having the structure AB.sub.x, in which A and B are the reactive groups, by step-growth polymerization, with random branching and without cross-linking. Kim, Y. H. et al, Journal of the American Chemical Society, Vol. 112, p. 4592 (1990) and U.S. Pat. No. 4,857,630 to Y. H. Kim, describe this kind of "single generation" approach in the preparation of hyperbranched polyphenylenes. U.S. Pat. No. 3,669,939 to Baker, A. S. et al teaches highly branched, non-crosslinked, aliphatic polyesters, prepared by a "single generation" melt condensation polymerization of monomers having a single carboxylic acid functionality and multiple alcohol functionalities. Hawker, C. J., Lee, R. and Frechet, M. J. M., Journal of the American Chemical Society, Vol. 113, No. 12, (1991) pp 4583-4588, teaches a single generation procedure for the preparation of all aromatic, highly-branched, non-cross-linked polyesters. In this procedure, 3,5-bis(trimethylsiloxy)benzoyl chloride is melt polymerized by the Kricheldorf method, described in H. R. Kricheldorf et al, Makromol. Chem. 184, 475 (1983), driving off trimethylsilylchloride. The product can be subjected to hydrolysis to provide phenolic terminated highly branched polyesters. This procedure has the shortcomings of requiring expensive, water-sensitive reactants and difficult monomer preparation steps. U.S. patent application Ser. No. 788,070, filed Nov. 11, 1991, by S. Richard Turner et al, teaches the preparation of multiply-branched polyesters by reacting compounds having the general structure HOOC--Ar--(O--CO--alkyl) (2 or 3) or having the general structure alkyl-CO--O--Ar--(COOH) (2 or 3). The above-discussed all-aliphatic branched polyesters of Baker et al and all-aromatic polymers of Hawker and Frechet et al and Turner et al have extremely divergent Tg's. The all-aliphatic polymers have very low Tg's, which limits use temperatures. The all-aromatic polymers have very high Tg's, which makes melt condensation and various polymer processing procedures difficult.